Gas Mileage Calculator

How to Accurately Measure Your MPG

Your car's sticker MPG and its real-world fuel economy are often very different numbers. The EPA tests under controlled lab conditions — your actual mileage depends on how, where, and when you drive.

The most reliable way to find your true fuel economy is the tank-to-tank method:

1. Fill your tank completely and reset your trip odometer (or note the mileage).
2. Drive normally until you need to refuel. Don't change your habits — the point is to measure your actual consumption.
3. Fill up again at the same pump if possible (this reduces measurement error from different auto-shutoff points).
4. Divide the miles driven by the gallons added. That's your real MPG for that tank.

Example: You drove 360 miles and put in 12 gallons → 360 ÷ 12 = 30 MPG.

For metric, multiply liters used by 100, then divide by kilometers: 42 L × 100 ÷ 600 km = 7.0 L/100km.

Why Your MPG Fluctuates

If your numbers vary from tank to tank, that's normal. Many factors affect fuel economy:

• City vs. highway. Stop-and-go driving uses far more fuel. A car rated 30 mpg highway might get only 22 in the city.
• Temperature. Cold weather thickens engine oil, increases tire resistance, and makes the engine take longer to reach its efficient operating temperature. Winter MPG can drop 15–25%.
• Terrain. Hilly routes consume more fuel than flat ones, even if the distance is the same.
• Passengers and cargo. Every extra 100 lbs costs roughly 1% in fuel economy.
• Ethanol content. E15 or E85 blends contain less energy per gallon than pure gasoline, which means lower MPG (but often at a lower price per gallon).

Track your MPG over 4–5 fill-ups to get a meaningful average. A single tank can be misleading due to any of the factors above.